EP2331926B1 - Method and device for determining a center of gravity of a motor vehicle - Google Patents

Description

State of the art

The invention relates to a method and a device for determining a center of gravity of a motor vehicle.

Motor vehicles are regularly equipped with safety functions and / or driving dynamics control functions, such as ESP. Since the motor vehicles, in particular with high loading variance, for example commercial vehicles, in the loaded state may have a very different driving behavior to the unloaded state, plays in many control functions, the position of the center of gravity of the motor vehicle, especially in the loaded state, as an input variable an important role.

From the DE 10 2004 056 108 A1 is a method for approximate determination of the center of gravity of a vehicle known. In this case, an estimated value for the center of gravity of the vehicle in the longitudinal direction is determined from the longitudinal forces of the wheels, the pitch angle of the road, the longitudinal acceleration of the vehicle and the wheel distance.

In this and other known methods, at least one spatial coordinate of the center of gravity is generally assumed to be known and fixed. Depending on the motor vehicle and the load of the motor vehicle, however, the center of gravity with respect to the center of the vehicle can be greatly displaced in all three spatial directions. This applies in particular to vans and / or vehicles loaded on a roof rack.

Disclosure of the invention

It is therefore the object of the present invention to provide a method and a device for determining a center of gravity of a motor vehicle with which the center of gravity can be determined simply and accurately.

This object is achieved according to the invention by the features specified in claim 1. Further embodiments of the invention will become apparent from the dependent claims.

An essential aspect of the invention is to determine two different values representing a drive force (hereinafter drive force values) for at least one wheel of the motor vehicle, as well as associated longitudinal acceleration values and associated wheel slip values. From these state variables, all three coordinates of the center of mass can be calculated simply and accurately. The specification of a certain coordinate is no longer necessary. Associated values should be understood here as those which are measured either simultaneously or in a timely manner with respect to the driving force values.

The center of mass is preferably the overall center of gravity of the motor vehicle including loading and possibly including one or more persons.

As coordinates of the center of gravity preferably a distance of the center of gravity to a rear axle of the motor vehicle, a height of the center of gravity and a lateral deviation of the center of gravity from a central longitudinal axis of the motor vehicle are used.

The exact knowledge of the center of gravity makes it possible to adapt driving safety systems and / or driving control systems to different loading conditions and thus to improve driving safety.

The different drive force values are preferably determined at different times. The times are preferably far apart, preferably at least a few seconds apart. The more different the driving situations, the more accurate is the result in principle.

The different drive force values can alternatively also be determined continuously over time.

In a further advantageous embodiment, the coordinates of the center of gravity are determined by means of a recursive identification algorithm. This contributes to the fact that the coordinates are determined particularly quickly and precisely. In this context, it is particularly advantageous if the coordinates are determined using the method of least squares (RLS), a Kalman filter and / or a UKF (Unscented Kalman filter). Depending on a number of state variables, for example, depending on the driving force values, the wheel slip values and / or the longitudinal acceleration values, the Kalman filter basically determines a preferably optimum parameterization of a function. The optimum parameterization is characterized, for example, by a minimum square of errors. The UKF is preferably used in strongly non-linear functions.

The coordinates of the center of gravity are preferably fed to a safety and / or control algorithm of the motor vehicle as an input variable.

Brief description of the drawings

Fig. 1

eine Vorrichtung zum Ermitteln eines Schwerpunktes des Kraftfahrzeugs,

Fig. 2

eine erste Gleichung zum Ermitteln zweier Koordinaten des Schwerpunktes,

Fig. 3

ein Gleichungssystem zum Ermitteln der Koordinaten des Schwerpunktes,

Fig. 4

ein Ablaufdiagramm eines Programms zum Ermitteln der Koordinaten des Schwerpunktes,

Fig. 5

sechs Diagramme.

The invention will now be described by way of example with reference to the accompanying drawings. Show it:

Fig. 1

a device for determining a center of gravity of the motor vehicle,

Fig. 2

a first equation for determining two coordinates of the center of gravity,

Fig. 3

a system of equations for determining the coordinates of the center of gravity,

Fig. 4

a flowchart of a program for determining the coordinates of the center of gravity,

Fig. 5

six diagrams.

Fig. 1 shows a device 2 ( FIG. 1 ) for determining a center of gravity of a motor vehicle, such. B. a controller. The device 2 comprises a recursive identification algorithm, for example an RLS, a Kalman filter or a UKF. These algorithms calculate one or more output variables by recursive identification, depending on several input variables, with output quantities gradually approaching the optimum values. The output variables are preferably parameters of formulas which are determined recursively.

At least driving force values F (from the engine control unit), wheel slip values A and longitudinal acceleration values a _{x are} supplied to the device 2 as input variables (or values representative of these variables). For example, driving or braking torques T are representative of the driving force values F. The driving force values F may also be negative, which in this case corresponds to a braking force.

As an output, the device 2 provides all three spatial coordinates of the center of gravity, z. B. a distance I _{R of} the center of gravity to a rear axle of the motor vehicle, a height h of the center of gravity and a lateral deviation y of the center of gravity of a central longitudinal axis of the motor vehicle. Alternatively, another reference coordinate system can be selected.

The coordinates h, I _R , y of the center of gravity are preferably fed to a safety and / or control algorithm of the motor vehicle as input variables. The functions mentioned (eg ESP, ABS, ASR, etc.) can thus be adapted to different loading conditions. At a precisely known distance I _R , for example, the function of an ABS system can be improved, from which the driving safety benefits.

A first equation ( FIG. 2 ) shows a simple relationship between the driving force values F _F , F _R determined on the basis of measured values on a wheel of a front axle or a rear axle of the motor vehicle, the associated wheel slip values λ _F , λ _R and longitudinal acceleration values a _{x of} the motor vehicle and two of the coordinates of the center of gravity , in particular the distance I _R and the height h. Furthermore go into this first equation the Gravitational acceleration g and a distance I between the front and rear axle of the motor vehicle. The first equation thus has two unknowns with the distance I _R and the height h. The first equation can not be solved by once determined input variables, in particular the driving force values F _F , F _R , the associated wheel slip values λ _F , λ _R and longitudinal acceleration values a _x . Therefore, the equation is solved by determining the driving force values F _F , F _R and the associated wheel slip values λ _F , λ _R and longitudinal acceleration values a _x at least two or more different times. This creates a solvable, preferably overdetermined system of equations with which the sought-for coordinates can be calculated very precisely. This first system of equations is preferably used when the center of gravity is in the gamma direction approximately in the middle of the motor vehicle. Further, another equation may be used which contains the γ coordinate and another coordinate as parameters and by means of which the lateral deviation y can be calculated.

According to Fig. 3 is z. B. a system of equations of four differential equations used, each describing the rotational acceleration of one of the four wheels of the motor vehicle. From each of the differential equations, all three coordinates h, I _R , y of the center of gravity could be calculated. However, the result becomes more accurate if at least two, preferably all equations z,. B. be solved by means of a recursive algorithm.

In these equations, the driving or braking torques T, in particular the driving or braking torques T _Fl , T _Fr , T _Rl , T _Rr front left or front right or rear left or rear right, representative of the driving force _values F. Der Partial fractional term (v (t) - (w (t) xr)) / v (t) occurring in all differential equations is representative of the wheel slip values λ, where the vehicle speed v, the wheel angular velocity ω, and the wheel radius r enter the fractional term received. In this case, the individual wheel angular velocities ω _Fl , ω _Fr , ω _Rl , ω _Rr again _relate to the wheel in the front left or front right or rear left or rear right. Further, in the equation, the inertia moments J _F , J _{R of} the front and rear wheels, the wheel angular accelerations ώ _Fl , ώ _Fr , ώ _Rl , ώ _Rr , the longitudinal stiffness c, the mass m of the motor vehicle, the wheel radius r, preferably the lateral acceleration ay and the gauge w. The longitudinal stiffness c is the proportionality constant for describing the proportionality between the driving forces and the wheel slip values λ. Preferably, a program for determining the coordinates h, I _R , y of the center of gravity is stored on a storage medium of the device 2 ( FIG. 4 ). The program is started in a step S1, for example, in a timely manner an engine start of an internal combustion engine of the motor vehicle, wherein optionally variables are initialized in step S1.

In a step S2 can be checked whether a predetermined condition CON is satisfied. The predetermined condition CON is preferably fulfilled when the motor vehicle is in a controlled driving situation, the wheel slip so z. B. is smaller than a predetermined threshold.

If the condition of step S2 is met (case y), steps S3, S4 and S5 are preferably performed in parallel or at least in a timely manner. If necessary, the step S2 is executed again if the condition of step S2 is not met.

In step S3, a first driving force value F1 is determined depending on a first wheel torque T1. The first wheel torque T1 can be measured, for example, with a torque sensor.

In step S4, a first longitudinal acceleration value a1 belonging to the first drive force value F1 is determined, for example, by means of an acceleration sensor. Alternatively, the first longitudinal acceleration value a1 may be determined by time derivative of the velocity v.

In step S5, a first wheel slip value λ1 associated with the first driving force value F1 is measured or estimated in a known manner.

The steps S6, S7 and S8 are processed in a corresponding manner after the steps S3, S4 and S5, wherein in the steps S6, S7 and S8 the second drive force value F2 depends on a second wheel torque T2, the associated second longitudinal acceleration value a2 and the associated second Radschlupfwert λ2 be determined.

In step S9, the coordinates h, I _R , y of the center of gravity are determined depending on the driving force values F1, F2, the longitudinal acceleration values a1, a2, and the wheel slip values λ1, λ2. This is preferably done on the basis of one of the formulas given in the FIGS. 2 and 3 are shown. Further measurements of driving force, longitudinal acceleration and wheel slip can follow.

After the step S9, the steps S3 to S8 can be executed again. Alternatively, the program may be terminated with step S10. The coordinates h, I _R , y of the center of gravity are preferably made available to a safety and / or control algorithm of the motor vehicle as input variables.

With this method, the center of gravity can be determined very precisely within a few seconds, as shown in Diagram 4, 6, 8, 10, 12, 14 ( FIG. 5 ) is recognizable. In particular, a first diagram 4 shows the speed v of the motor vehicle and the wheel angular velocities ω _Fl , ω _Fr , ω _Rl , ω _Rr , as a function of the time t. As the velocities v, ω _Fl ω _Fr , ω _Rl , ω _{Rr become} smaller, the first diagram 4 shows a braking operation of almost 30 m / s to 5 m / s. The individual values are so close to each other that only a thick line can be seen. This is representative of the wheels running stably. This stable running of the wheels can be assumed as the starting condition for an algorithm for determining the coordinates h, I _R , y of the center of gravity, in particular as a condition CON in the program for determining the coordinates h, I _R , y of the center of gravity.

During the braking process shown in the first diagram 4 occurs at the wheels of the rear axle, a wheel torque T _Rl , T _Rr between 0 and -1000 Nm, and at the wheels of the front axle, a wheel torque T _Fl , T _Fr between 0 and about -1800 Nm on what is shown in a second diagram 6.

The occurring wheel torques T _R1 , T _Rr T _Fl , T _Fr cause a longitudinal acceleration (deceleration) a _x , which is shown in a third diagram 8 and which is between 0 and -5 m / s ² .

The device 2, as shown in a fourth diagram 10, provides the distance I _{R of} the center of gravity to the rear axle in seconds, as shown in a fifth diagram 12, the lateral deviation y of Center of gravity and, as shown in a sixth diagram 14, the height h of the center of gravity, wherein the determined coordinates h, I _R , y gradually approach the actual coordinates h_tat, I _R _tat, y_tat shown in dashed lines.

Claims (9)

1. Method for determining the centre of gravity of a motor vehicle, in which

   - two different drive force values (F, T) are determined for at least one wheel of the motor vehicle,

   - and associated longitudinal acceleration values (a_x) and

   - associated wheel slip values (λ) are determined,

   characterized in that
   at least two coordinates (h, l_r, y) of the centre of gravity are determined from the determined drive force values (F, T), the associated longitudinal acceleration values (a_x) and the associated wheel slip values (λ).
2. Method according to Claim 1, in which the different drive force values (F, T) are determined at different times.
3. Method according to Claim 2, in which the different drive force values (F, T) are determined continuously.
4. Method according to one of the preceding claims, in which the coordinates (h, l_r, y) of the centre of gravity are determined by means of a recursive estimation algorithm.
5. Method according to Claim 4, in which the coordinates (h, l_r, y) of the centre of gravity are determined by means of the least squares method (RLS).
6. Method according to Claim 4, in which the coordinates (h, l_r, y) of the centre of gravity are determined by means of a Kalman filter.
7. Method according to Claim 6, in which the coordinates (h, l_r, y) of the centre of gravity are determined by means of an unscented Kalman filter (UKF).
8. Method according to one of the preceding claims, in which the coordinates of the centre of gravity are fed to a safety and/or control algorithm of the motor vehicle.
9. Device for determining a centre of gravity of a motor vehicle which is designed to process the method according to one of the preceding claims.

Images